The quoting problem can be resolved by implementing SGML's
minimizations. The markup would then look a lot more like
a REBOL object -- for example, appropriate DTD declarations
can make many end tags optional in SGML

Yes, that is a good point. But then, I can do the same with any parser
compiler like YACC, etc. The question is, why should I be required to do
that? If people think XML is complex, SGML is much more so (and indeed
more powerful).

I think the question comes down to simply this: what level of
complexity are you willing to deal with to create distributed
applications?

At least for me, I would like to focus my attention on the application
itself not on creating and debugging endless descriptions of metadata.

I should clarify that my XML article was not meant to say that XML will
be replaced any day soon nor to imply that REBOL will replace it. What
I really want to communicate is that we don't need to make everything
complex all the time. There are times when simple solutions work quite
well. I think massively successfull designs of all kinds such as HTTP, CGI, Google, and others prove that simpler is better. If people can understand it, they are more likely to use it.

The proliferation of markup languages like HTML, XHTML, DHTML, SHTML,
XSL, etc. and the differences between them exposes the complexity flaw
of the entire markup technique.

I think it is quite ironic that the document type definition (DTD) used
on modern markup documents does not even use the standard markup method
itself. For example, the first line of a document has:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">

Rather than using a markup directly (like you might use for an HTML
<meta> tag), the quoted string requires another sub-language that
is not at all like markup. Now code needs to parse -//W3C//DTD HTML 4.01//EN
too.

REBOL also includes a type of "document" header. All content begins with
a REBOL header that is itself written in REBOL, not some other language:

The benefit of course is that we do not require yet another language
to parse and process these headers.

If your reply is that, "well, the DTD is an exception to the case",
then what's the excuse for CSS? That's yet another and different language
buried within XML/HTML (and I emphasize ML here) definition. You write:

The so-called "perfect way" of expressing information (XML) does not
even use it's own pure lexical form for the expression of CSS
information. (Or, saying it in REBOL words: CSS is not a dialect of
XML.) I would not be at all surprised to discover that the creators of
CSS, during their design phase, decided that they wanted to avoid the
overly complicated, inefficient style of XML.